1. Field of the Invention
The present invention relates to a spring fixture that attaches a heat sink to a substrate for multiple cycle assembly/disassembly.
2. Background Information
Integrated circuit packages generate heat which must be removed from the circuits. To help remove this heat, these packages conventionally are thermally coupled to a heat sink. A heat sink typically contain a plurality of fins that extend from a pedestal having a mounting surface. This mounting surface mates with a corresponding surface of an integrated circuit package to form a mating surface. The mating surface must be relatively flat to insure that there are no air voids when the components are assembled. Air voids will significantly increase the thermal impedance between the heat sink and the integrated circuit package.
Stringent flatness requirements for individual parts of the electrical assembly increase the cost of producing the heat sink and the overall assembly. One known technique to reduce the stringent flatness requirements of the heat sink is to press the heat sink into the integrated circuit package by a clip having four L-shaped ears. U.S. patent application Ser. No. 09/110,539, filed on Jul. 6, 1998, owned by the assignee of this patent application, and entitled "An Electrical Assembly That Includes A Heat Sink Which Is Attached To A Substrate By A Clip" is directed to an electrical cartridge containing integrated circuit packages that employs a clip having four L-shaped ears to attach a heat sink to a substrate.
FIG. 1 shows an electrical assembly 10 of U.S. patent application Ser. No. 09/110,539. The electrical assembly 10 includes an electronic assembly 12 that includes an integrated circuit package 14 having a silicone integrated circuit (not shown). The integrated circuit package 14 is mounted to a substrate 16. The electrical assembly 10 further has a heat sink 18 that is mounted to the substrate 16. The heat sink 18 is pressed into the integrated circuit package 14 to provide a thermal path for the heat generated by the integrated circuit. The assembly 10 includes a clip 20 that attaches the heat sink 18 to the substrate 16.
The clip 20 is shown with four L-shaped ears 22 that are inserted through clearance holes 24 in the substrate 16 and corresponding attachment holes 26 in the heat sink 18. The four L-shaped ears 22 extend from a center plate portion 28. The L-shaped ears 22 are bent during insertion through the holes 24 and 26. Once beyond the attachment holes 26 of the heat sink 18, the L-shaped ears 22 snap back so as to permit the clip 20 to exert a spring force that pushes the heat sink 18 into the integrated circuit package 14.
However, from one electrical assembly 10 to the next, this spring force from L-shaped ears 22 is not consistent due to the variations within part manufacturing tolerances. Moreover, the L-shaped ear technique does not permit a worker to adjust the spring force from L-shaped ears 22 so as to evenly distribute this force over the surface of the substrate 16. Without an even distribution of force, the substrate 16 is more likely to bend which may cause the substrate 16 or the silicone integrated circuit within the integrated circuit package 14 to crack.
It would be desirable to provide an electrical assembly that permits even distribution of compression forces generated in pressing a heat sink into an integrated circuit package.